1. Field of the Invention
The present invention is directed to an image processing technique and more particularly, to an image processing method to keep natural appearance of a noise-reduced image.
2. Description of Related Art
In a digital camera application, noise-reducing is very important and critical process to a digital image captured in high ISO mode. After the noise-reducing process, it often happens that detailed textures together with gradient lighting changes of an object itself in a digital image are also blurred or disappear, such that the digital image become un-natural.
In order to keep a natural appearance for the digital image, a post process performed on a noise-reduced image generally adopts an image sharpness algorithm to enhance edges of an object in the image to achieve a sharpening effect. In order to deal with a side-effect that the natural appearance disappears after the noise-reducing process, a method which is generally adopted is to adjust parameters in the noise-reducing process to mitigate the side-effect of noise-reduction and to assign different noise-reducing parameters for a smoothing area, a texture area or a sharpness edge of the image while noise-reducing.
For overly blurry images after being noise-reduction, the sharpness algorithm may be utilized to sharpen the object edges or the texture area to increase the image details. However, during the noise-reducing process, the method of assigning different parameters according to the difference of the smoothing area, which would result in a larger difference between the smooth area and the texture area or the sharpness edge of the image. As a result, the processed image would look unnatural. Further, if the noise-reducing parameters are adjusted to mitigate the difference between each area, a problem that the noise cannot be clearly reduced. Accordingly, how to keep the natural appearance of the noise-reduced image has become a subject to be solved.